FIG. 1
FIG. 1 shows a conventional single-router wireless packet data network 100. A packet router 102 receives data packets from the remainder of a network 104 and routes them to one or more network access points 106-110. The network access points 106-110 transmit the packets forward to a user terminal 112 over forward wireless links 114-116. The user terminal 112 transmits packets back to the network access points 106-110 over reverse wireless links 118-120. The user terminal 112 may be a cellular telephone carried by a person, a portable computer, a mobile telephone in an automobile, or any other mobile device which must continue to provide connectivity even while it moves.
A control point 122 is connected to the packet router 102. It manages the wireless links 114-120. Management includes many functions. For example, as the user terminal 112 moves around the path loss between it and the network access points 106-110 changes. In the situation shown in FIG. 1, the control point 122 must cause the user terminal 112 to transmit with the minimum amount of power required to be received by at least one of network access points 106-108. Mobile station transmit power is minimized since it causes interference to transmissions from other mobile stations. When the user terminal moves from the area served by network access point 106 to the area served by network access point 108, there will be a handoff of the user terminal 112 from network access point 106 to network access point 108. The control point 122 must manage the handoff. Other management functions are known to those with skill in the art.
FIG. 2
FIG. 2 shows a conventional multiple-router wireless packet data network 200 supporting a mobility protocol such as Mobile IP as described in the Internet Engineering Task Force RFC 2002. A second packet router 202 is connected to the first packet router 102, to the rest of the network 104, or (as shown) to both. Second packet router 202 is connected to network access points 204-206. In FIG. 2, the user terminal 112 is moving from the area served by network access point 110 (where it is served by forward link 208) to the area served by network access point 204 (where it is served by forward link 210). Control point 122 manages the wireless links during this handoff (including the management of reverse links 212-214) in much the same way as during the handoff shown in FIG. 1. If desired, control can be passed from first control point 122 to second control point 222. These control points are connected to first and second packet routers 102 and 202, respectively.
FIG. 2 also shows a home agent 224 and a foreign agent 226. Home agent 224 is connected to first packet router 102, and foreign agent 226 is connected to second packet router 202.
User terminal 112 has a network address for which packet router 102 advertises reachability. A packet intended for user terminal 112 is therefore sent to first packet router 102. When user terminal 112 is in the coverage area of network access points associated with packet router 102 (106-110), packet router 102 will forward the packet to control point 122 which will send the packet for transmission to the network access points that currently provide a forward wireless link to the user terminal 112.
User terminal 112 may leave the area served by first packet router 102 and may enter the area served by second packet router 202. The net 104 will send packets destined to user terminal 112 to packet router 102 which will then forward them to home agent 224 which maintains track of user terminal 112's current location in the form of a "care-of" address. The home agent will then encapsulate these packets in packets destined to the care-of address of the user terminal (e.g., foreign agent 226) and send these packets through packet routers 102 and 202. Upon receiving these packets, foreign agent 226 will de-capsulate the packets and forward the packets destined for transmission to user terminal 112 to control point 222. Control point 222 will then forward the packets for transmission to the network access points that currently provide a forward wireless link to the user terminal 112.
In this method, control of the network access points for a data connection has moved from control point 122 to control point 222. In another conventional method, control does not move between the two control points, in which case packet router 102 continues to forward packets for transmission to user terminal 112 to control point 122 which then sends the packets directly to whatever network access points provide a forward wireless link to user terminal 112, regardless of the system in which these network access points are located. E.g., control point 122 may forward packets for transmission to network access points 106-110 as well as 204-206.
This architecture suffers from several fundamental problems: the control points for each part of the network are single points of failure which must be made highly reliable, increasing their cost. Furthermore, since they are unique for each network, the architecture does not scale well as the number of network access points increase, increasing with it the population of mobile terminals that can be served and consequently, the load presented to the control points. Last, emerging high speed wireless protocols require low-latency control by the control point which is not possible due to the transmission and queuing delays between the control points and the network access points.